Distinctive prokaryotic microbiomes in sympatric plant roots from a Yucatan cenote.

OBJECTIVE: Cenotes are flooded caves in Mexico's Yucatan peninsula. Many cenotes are interconnected in an underground network of pools and streams forming a vast belowground aquifer across most of the peninsula. Many plants in the peninsula grow roots that reach the cenotes water and live submerged in conditions similar to hydroponics. Our objective was to study the microbial community associated with these submerged roots of the Sac Actun cenote. We accomplished this objective by profiling the root prokaryotic community using 16S rRNA gene amplification and sequencing. RESULTS: We identified plant species by DNA barcoding the total genomic DNA of each root. We found a distinctive composition of the root and water bacterial and archaeal communities. Prokaryotic diversity was higher in all plant roots than in the surrounding freshwater, suggesting that plants in the cenotes may attract and select microorganisms from soil and freshwater, and may also harbor vertically transmitted lineages. The reported data are of interest for studies targeting biodiversity in general and root-microbial ecological interactions specifically.

Saliva is a reliable and accessible source for the detection of SARS-CoV-2.

OBJECTIVES: The aim of this study was to investigate the feasibility of saliva sampling as a non-invasive and safer tool to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and to compare its reproducibility and sensitivity with nasopharyngeal swab samples (NPS). The use of sample pools was also investigated. METHODS: A total of 2107 paired samples were collected from asymptomatic healthcare and office workers in Mexico City. Sixty of these samples were also analyzed in two other independent laboratories for concordance analysis. Sample processing and analysis of virus genetic material were performed according to standard protocols described elsewhere. A pooling analysis was performed by analyzing the saliva pool and the individual pool components. RESULTS: The concordance between NPS and saliva results was 95.2% (kappa 0.727, p = 0.0001) and 97.9% without considering inconclusive results (kappa 0.852, p = 0.0001). Saliva had a lower number of inconclusive results than NPS (0.9% vs 1.9%). Furthermore, saliva showed a significantly higher concentration of both total RNA and viral copies than NPS. Comparison of our results with those of the other two laboratories showed 100% and 97% concordance. Saliva samples are stable without the use of any preservative, and a positive SARS-CoV-2 sample can be detected 5, 10, and 15 days after collection when the sample is stored at 4 °C. CONCLUSIONS: The study results indicate that saliva is as effective as NPS for the identification of SARS-CoV-2-infected asymptomatic patients. Sample pooling facilitates the analysis of a larger number of samples, with the benefit of cost reduction.

Plastid DNA diversity is higher in the island endemic Guadalupe cypress than in the continental Tecate cypress.

BACKGROUND: Callitropsis guadalupensis (Guadalupe cypress) is endemic to Guadalupe Island, Mexico, where it is the dominant species of the only forest. The species has suffered declining numbers following the introduction of goats to the island over 150 years ago. Callitropsis guadalupensis is closely related to Callitropsis forbesii (Tecate cypress), distributed in small isolated populations in mainland Baja California and southern California. The objective of the present study was to compare the genetic diversity of the island endemic to the continental species. METHODOLOGY/PRINCIPAL FINDINGS: We measured genetic diversity in Callitropsis guadalupensis (n =54) from Guadalupe Island and in Callitropsis forbesii (n = 100) from five populations in mainland Baja California. The plastid DNA trnS-trnG spacer and the trnL-trnF region were chosen for characterization. Thirty-four haplotypes were observed, of which six were shared between both species. One of these haplotypes was also shared with three other species, Callitropsis lusitanica, Callitropsis montana, and Callitropsis stephensonii. Haplotype diversity (h) and nucleotide diversity (π) were significantly higher for Callitropsis guadalupensis (h = 0.698, π = 0.00071) than for Callitropsis forbesii (h = 0.337, π = 0.00024). CONCLUSIONS/SIGNIFICANCE: Callitropsis guadalupensis shows no evidence of a founder effect or of a genetic bottleneck, and can be added to a growing list of insular species with higher genetic diversity than their mainland relatives.

Tropical montane nymphalids in Mexico: DNA barcodes reveal greater diversity.

MATERIALS AND METHODS: DNA sequences obtained for the Barcode of Life library in the All Lepidoptera Campaign project Nymphalidae of Central Mexico were analyzed as a test of species limits and to explore possible phylogenetic groupings in the Preponini tribe. Using specimens in the National Insect Collection of the Instituto de Biología of the Universidad Nacional Autónoma de México, 78 specimens were assayed for cytochrome oxidase c subunit 1. RESULTS: Disregarding the missing data, there were 458 conserved sites, 200 variable sites and 187 parsimony-informative sites. The neighbor-joining and maximum likelihood analyses indicate that none of the three genera of Preponini as currently circumscribed are reciprocally monophyletic. As per species limits, high levels of barcode variation in the Prepona deiphile complex suggest the existence of at least two new endemic species to Mexico. The divergent taxa were escalantiana from the Tuxtlas region in Veracruz, and ibarra from Sierra Madre del Sur in the Pacific states of southern Mexico. The genetic distance in the CO1 fragment between them and the other deiphile populations ranged from 2.7 to 8.0%. CONCLUSION: We recommend that morphological data need to be re-examined and that additional molecular data for species ought to be gathered before a particular biogeographic model can be proposed for the group in Mesoamerica.